Casing mounted sensors, actuators and generators

ABSTRACT

A casing sensor and methods for sensing using a casing sensor are disclosed. The casing sensor includes a casing shoe and a sensor coupled to the casing shoe. A casing data relay includes a downhole receiver coupled to a well casing and a transmitter coupled to the receiver. The casing sensor may be coupled to the transmitter. A drill string actuator may be controllable through the downhole receiver.

FIELD OF THE INVENTION

This invention relates generally to a method and apparatus forcollecting data regarding geological properties of underground orundersea formations in the vicinity of a well bore under construction.More particularly, this invention relates to a method and apparatus forcollecting data regarding the formations during and after drilling andconstructing the well bore. In particular, the invention relates to amethod and apparatus for collecting data regarding the formationssensors, actuators and generators coupled to a well casing inside thewell bore. This invention also relates to a method and apparatus forrelaying data collected deep in a well to the surface.

BACKGROUND OF THE INVENTION

Geologists and geophysicists collect data regarding undergroundformations in order to predict the location of hydrocarbons such as oiland gas. Traditionally, such information is gathered during anexploration phase. In recent years, however, the art has advanced toallow the collection of geophysical and geological data as a well isbeing drilled.

For example, in Vertical Seismic Profiling (“VSP”), drilling operationsare interrupted to place a series of seismic sensors at discrete depthsin a borehole. A surface source releases energy that is reflected offunderground geological formations. The seismic sensors in the boreholesense the reflected energy and provide signals representing reflectionsto the surface for analysis.

In a subsequent development, known as “drill bit seismic”, seismicsensors are positioned at the surface near the borehole to sense seismicenergy imparted to the earth by the drill bit during drilling. Thissensed energy is used in the traditional seismic way to detectreflections from underground geological formations. Further, thistechnique is used to detect “shadows”, or reduced seismic energymagnitude, caused by underground formations, such as gas reservoirs,between the drill bit and the surface sensors.

A greatly simplified description of those steps involved in drilling anoil well follows. A portion of the oil well is drilled using a drillstring consisting of drill pipe, drill collars and drill bit. After aportion of the well has been drilled, a section of casing, or large borepipe, is inserted into the well bore and cemented for, among otherthings, zonal isolation. Casing performs a number of functions,including: preventing the bore hole from caving in; preventing fluids inthe bore hole from contaminating the surrounding formations; preventingthe introduction of water into the surrounding formations; containingany production from the well; facilitating pressure control; providingan environment for the installation of production equipment; andproviding zonal isolation.

When the casing is in place it is cemented to the formation wall. Thisis accomplished by pumping cement through the casing until it exits atthe end of the casing through a special section of casing called a“casing shoe” and flows up the annulus between the casing and the wallof the well bore. The concrete is then allowed to set.

In subsequent drilling operations, the deep end of the newly cementedcasing is drilled out and another section of the well bore is drilled.The process of drilling sections of the well bore followed by insertingand cementing well casing repeats until the desired well depth isreached.

As the well bore is being drilled, drilling fluids, known as “mud”, arepumped into the drill string. The mud travels down the drill stringuntil it is ejected. The mud picks up cuttings and carries them to thesurface. The specific gravity of the drill mud is carefully controlledso that the weight of the column of mud is (1) large enough to preventgas or other hydrocarbons from entering the borehole from thesurrounding formations; (2) without exerting so much pressure that thesurrounding formations are damaged.

After each section of casing is laid and cemented in, the fracturepressure of the formation just below the end of the casing is measured.Generally, the fracture pressure of deeper formations is greater thanthe fracture pressure of shallower formations. The specific gravity ofthe drilling mud is subsequently controlled to make sure that thepressure on the formation at the end of the casing does not exceed thefracture pressure of the formation at that point. This is generallyaccomplished by calculations incorporating the measured specific gravityof the drilling mud and the depth of the column of drilling mud abovethe formation.

Downhole data are captured using “wireline” techniques in which, priorto casing being laid, a tool, such as an acoustic logging tool, islowered into the well bore and slowly retrieved, gathering data andstoring it or transmitting it to the surface as the tool is beingretrieved. Alternatively, measurement while drilling (“MWD”) or loggingwhile drilling (“LWD”) tools are attached to the drill string just abovethe drill bit and drill collars. These generally expensive tools gatherdata during the drilling process and store it or transmit it to thesurface.

SUMMARY OF THE INVENTION

In general, in one aspect, the invention features a casing sensorcomprising a casing shoe and a sensor coupled to the casing shoe.

Implementations of the invention may include one or more of thefollowing. The sensor may comprise a pressure sensor. The sensorpressure may comprise a pressure transducer and a transmitter coupled tothe pressure transducer. The casing sensor may comprise a surfacereceiver coupled to the transmitter. The casing sensor may comprise adrill string through the casing shoe.

In general, in another aspect, the invention features a casing datarelay comprising a downhole receiver coupled to a well casing and atransmitter coupled to the receiver.

Implementations of the invention may include one or more of thefollowing. The casing data relay may comprise a surface receiver coupledto the transmitter. The surface receiver may be electrically oroptically coupled to the transmitter. The surface receiver may becoupled to the transmitter by electromagnetic telemetry. The surfacereceiver may be coupled to the transmitter by a pressure transducer. Thecasing data relay may comprise an antenna coupled to the downholereceiver, the antenna being configured to receive electromagneticradiation. The casing data relay may comprise one or more casing sensorscoupled to the casing, wherein one or more of the one or more casingsensors are coupled to the transmitter. The casing data relay maycomprise one or more drill string sensors coupled to a drill string. Atleast a portion of the drill string may be inserted through the casing.The drill string sensors may be coupled to the downhole receiver. One ormore of the drill string sensors may be coupled to the downhole receiverthrough a drill string transmitter. The casing data relay may comprisedrill string instruments coupled to the transmitter and a surfacetransmitter coupled to the downhole receiver. The casing data relay maycomprise a drill string actuator. The drill string actuator may becontrollable through the downhole receiver. The drill string actuatormay be configured to change a position of an adjustable gaugestabilizer. The drill string actuator may be configured to change a bitnozzle size.

In general, in another aspect, the invention features a method forcollecting geological data comprising sensing one or more geologicalparameters during drilling using one or more sensors coupled to a wellcasing in a well bore, collecting data from the one or more sensors andtransmitting the data to the surface. Sensing may comprise sensing usingone or more sensors coupled to a casing shoe, sensing using a pressuretransducer on a casing shoe, sensing pressure, sensing temperature,sensing acoustic energy, sensing stress or sensing strain. The methodmay further comprise transmitting acoustic energy. Transmitting maycomprise transmitting the data to the surface through a relay.

In general, in another aspect, the invention features a method formaintaining the integrity of a formation in the vicinity of a casingshoe comprising measuring well bore pressure in the vicinity of thecasing shoe during drilling.

Implementations of the invention may include one or more of thefollowing. The method may comprise transmitting data representing themeasured well bore pressure to the surface.

In general, in another aspect, the invention features a method forpositioning look ahead sensors comprising positioning acoustic sensorsalong a casing string.

In general, in another aspect, the invention features a method formonitoring well control events comprising monitoring pressure at two ormore locations inside a casing of the well.

Implementations of the invention may include one or more of thefollowing. Monitoring may comprise monitoring pressure at two or morelocations that are longitudinally displaced along the casing.

In general, in another aspect, the invention features a method fordetermining whether cement in a well borehole has cured comprisingpositioning a temperature sensor on a casing and monitoring thetemperature of the cement using the temperature sensor.

Implementations of the invention may include one or more of thefollowing. Positioning may comprise positioning the temperature sensorinside the casing or positioning the temperature sensor on the casingshoe.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a cross-section view of a drilling operation.

FIG. 2 is a cross-section view of casing being inserted into a well.

FIG. 3 is a perspective view of a section of casing according to thepresent invention.

FIG. 4 is a perspective view of a section of casing according to thepresent invention during the cementing operation.

FIG. 5 is a perspective view of a section of casing according to thepresent invention.

FIG. 6 is a perspective view of a section of casing according to thepresent invention after drilling has pierced the end of the casing.

FIG. 7 is a block diagram of a system according to the presentinvention.

FIG. 8 is a block diagram of a system according to the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

An apparatus for monitoring geological properties and drillingparameters and for facilitating seismic while drilling comprisessensors, actuators and generators coupled to the casing. The sensorsallow the collection and transmission to the surface of geological dataand critical drilling parameters (such as hydraulic measurements,downhole weight on bit, and downhole torque) from shortly after thecasing is inserted until the data is no longer needed. The actuators andgenerators facilitate the collection of data and are controllable fromthe surface. The apparatus also provides a relay for data transmittedfrom deeper in the well bore or from MWD or LWD tools. The equipmentrelays data between the surface and the sensors, actuators andgenerators deep in the well.

As shown in FIG. 1, a drilling rig 10 (simplified to exclude items notimportant to this application) comprises a derrick 12, derrick floor 14,draw works 16, hook 18, swivel 20, kelly joint 22, rotary table 24,drillstring 26, drill collar 28, LWD tool 30, LWD tool 32 and drill bit34. Mud is injected into the swivel by a mud supply line 38. The mudtravels through the kelly joint 22, drillstring 26, drill collars 28,and LWD tools 30 and 32 and exits through jets or nozzles in the drillbit 34. The mud then flows up the borehole 40. A mud return line 42returns mud from the borehole 40 and circulates it to a mud pit (notshown) and back to the mud supply line 38. The combination of the drillcollar 28, LWD tool 30, LWD tool 32 and drill bit 34 is known as thebottomhole assembly 36 (or “BHA”).

The data collected by the LWD tools 30 and 32 is returned to the surfacefor analysis by, for example, telemetry transmitted through the drillingmud. A telemetry transmitter 44 located in a drill collar or in one ofthe LWD tools collects data from the LWD tools and modulates the data totransmit it through the mud. A telemetry sensor 46 on the surfacedetects the telemetry and returns it to a demodulator 48. Thedemodulator 48 demodulates the data and provides it to computingequipment 50 where the data is analyzed to extract useful information.

After the well has been drilled to a certain depth, has shown in FIG. 2,a length of casing 52 is lowered into the well bore in sections. Thefirst section 54, called a “casing shoe”, has a specialized purpose, aswill be discussed below. As it is being lowered, the section of casingis suspended from casing hangar 56, which hangs from the hook 18.

When the casing 52 has been fully inserted into the borehole, as shownin FIG. 3, the casing shoe 54 comes to rest at or near the bottom of thewell bore. A centralizer 58 keeps the casing centered in the borehole.Signal-carrying cable 60 connects a cable tie-in 62 to equipment on thesurface. The cable 60 and cable tie-in 62 allow a connection between thesurface and sensors, actuators and generators in the casing shoe, aswill be discussed below. Further, cable 60 provides connections betweensensors, actuators and generators located along the casing (not shown inFIG. 3) to the casing shoe 54. Wireline anchor bands 64 secure the cable60 to the casing.

After the casing is position, it is cemented into place, as shown inFIG. 4. Cement is pumped down through the casing to the casing shoewhere it escapes through port 66. The cement 68 flows up the annulusbetween the casing and the surrounding formations 70.

When sufficient concrete has been poured to serve its intended purpose,the concrete is allowed to set, as shown in FIG. 5. As concrete sets,its temperature varies. By monitoring the temperature of the concreteusing temperature sensor 72, personnel at the surface can determine whenthe concrete has set sufficiently to go into the next step in thedrilling process. Information from the temperature sensor 72 istransferred to the surface through cable tie-in 62 and cable 60.Additional temperature sensors may be placed at other locations tomonitor the temperature of the concrete.

The next step in the drilling process, shown in FIG. 6, is to drill outcasing 52. Drill bit 74 penetrates the end of casing shoe 54 andcontinues the well bore. As drilling continues, mud is pumped downthrough the center of the drillstring 76 and out jets or nozzles in thedrill bit 74. The mud 78 picks up cuttings and carries them back tosurface along the annulus between the drill string and formation andthen along the annulus between the drillstring 76 and casing 52.

As discussed above, the specific gravity of the mud is carefullycontrolled to assure that the pressure exerted by the mud on theformation does not exceed the fracture pressure of formation. Thepressure exerted by the mud on the formation is monitored by a pressuresensor 80 located in the casing shoe. Its location in the casing shoeallows pressure sensor 80 to monitor the pressure on the weakestformation just below the casing shoe.

Personnel on the surface monitor the signals from the pressure sensor,which are sent to the surface through the cable tie-in 62 and cable 60.If they determine that the specific gravity of the mud must be increasedbecause of the danger of a “kick”, or influx of formation fluids intothe borehole, and the planned increase will raise the pressure exertedby the mud beyond the fracture pressure of the formation, they maydecide to stop drilling and insert another section of casing.

In addition to the pressure sensor and temperature sensor that werediscussed above, additional sensors are located along the casing toprovide a variety of other functions. For example, an array of acousticsensors and/or geophones may be located along a portion of the casing toreceive acoustic energy from the formation through the concretesurrounding the casing. Such acoustic sensors could be used inconjunction with acoustic energy generators located in the MWD tools foraccomplishing MWD acoustic logging. The acoustic energy generator couldbe attached to the casing, allowing long term monitoring of the acousticcharacteristics of the formations surrounding the borehole. An acousticenergy generator attached to the casing could also be used as a sourcefor acoustic energy measurements in another nearby well.

Similarly, the acoustic sensors could be used to detect acoustic energygenerated by surface generators or by acoustic sources in other nearbywells. The acoustic sensors could be used during drilling and after thewell is completed and is in production or after it has been shut in.

Acoustic sensors coupled to the casing can also be used in support of“look-ahead” technology, in which acoustic signals are used to detectgeological features ahead of the drill bit. With the acoustic sensorscoupled to the casing, the look-ahead performance improves over alook-ahead system employing surface acoustic sensors because theacoustic sensors coupled to the casing are closer to the geologicalfeatures being detected.

In addition to pressure sensors, temperature sensors and acousticsensors and generators, stress and strain sensors may be located alongthe casing to measure the stress and strain to be experienced by theformations surrounding the casing. Again, the stress sensors and strainsensors can be used during drilling and after the well has beencompleted and has been placed in production or has been shut in.

In another application of sensors, two or more pressure sensors could bestrategically located at various depths along the inside of the casing.Such an arrangement of pressure sensors could detect the dynamic changesin pressure associated with a kick. For example, detection of droppingpressure at successively shallower pressure sensors could indicate thata gas kick has occurred. Advance warning of such an event would allowpersonnel on the surface to engage blowout preventers to reduce thechance of injury to the surface equipment or personnel.

In general, any sensor that provides useful information regarding theformations surrounding the well can be attached to the casing. Further,any actuator or generator that produces useful signals, energy oractions to be used in measuring the properties of the formations or inmonitoring the drilling process may also be attached to the casing.

The placement of the sensors, actuators and generators is illustrated inFIG. 7. The well shown in FIG. 7 includes a surface casing 82, anintermediate casing 84, and a drill string 86. A set of surface casingsensors, actuators and generators 88 is coupled to the surface casing82. A set of intermediate casing sensors, actuators and generators 90 iscoupled to the intermediate casing 84. Depending on their purpose, thesensors, actuators and generators may be attached to the inside of thecasing or the outside of the casing. The sensors, actuators andgenerators may be welded to the casing or attached by bands or throughspecial annular fittings that affix them to the inside or the outside ofthe casing in such a way that they do not interrupt the flow of fluidsthrough or around the casing.

A set of MWD tool sensors, actuators and generators 92 is coupled to thedrill string 86. For example, if the MWD tool is an acoustic-loggingtool, it would include acoustic energy generators (transmitters) andacoustic energy sensors (receivers). Other types of tools would includeother types of sensors and generators. The MWD tool sensors, actuatorsand generators 92 may provide, for example, the capability to change theposition of an adjustable gauge stabilizer or to change the bit nozzlesize or to activate any actuator attached to the drill string.

The sensors, actuators and generators communicate with the surface inone or more of several ways. First, each sensor, actuator or generatormay have a cable connection to the surface. For example, the surfacecasing sensors, actuators and generators 88 may communicate with surfaceequipment 94 via cable 96 and the intermediate casing sensors, actuatorsand generators 90 may communicate with the surface equipment 94 viacable 98. Alternatively, some or all of the surface casing sensors,actuators and generators 88 may communicate with a surface casingcontroller 100, coupled to the surface casing 82, which gathers dataprovided by the surface casing sensors, formats it and communicates itto the surface equipment 94 via cable 98. Surface equipment 94 maytransmit commands or other data to the surface casing sensors, actuatorsand generators 88 directly or through the surface casing controller 100.

Similarly, some or all of the intermediate casing sensors, actuators andgenerators 90 may communicate with an intermediate casing controller102, coupled to the intermediate casing 84, which gathers data providedby the intermediate casing sensors, formats it and transmits it to thesurface equipment 94. Surface equipment 94 may transmit commands orother data to the intermediate casing sensors, actuators and generators90 directly or through the intermediate casing controller 102.

Cables 96 and 98 can be any kind of cable, including electrical cable oroptical fiber cable. Further, the information carried by the cable canbe sent using any information transmission scheme, including baseband,modulated (amplitude modulation, frequency modulation, phase modulation,pulse modulation or any other modulation scheme), and multiplexed(time-division multiplexed, frequency-division multiplexed or any othermultiplexing scheme, including the use of spread spectrum techniques).Consequently, each sensor, actuator or generator may communicate withthe surface equipment via its own communication media which is part ofcables 96 and 98 or each set 88 and 90 may share a communication mediathat is part of cables 96 and 98, respectively. Further, cables 96 and98 may be coupled to allow the surface casing sensors, actuators andgenerators to share the use of the communication medium formed by thecombination of the two cables 96 and 98.

Alternatively, communication between the surface casing controller 100and the surface equipment 94 may be by radio frequency transmission orpulse telemetry transmission. In the case of radio frequencytransmission, an antenna 104 extends from the surface casing controller100 that allows radio frequency communication between it and the surfaceequipment 94, which would communicate the RF energy via an antenna 106.In the case of pulse telemetry transmission, the surface casingcontroller 100 and the surface equipment 94 each include a transducer108 and 110 (see FIG. 8), respectively, that convert data into acousticpulses and vice versa. The acoustic energy travels through the casing82, the mud or any other medium that will allow the transmission ofacoustic energy. The RF energy and the acoustic energy can be modulatedor multiplexed in any of the ways described above. Further, thecommunication between the surface casing controller 100 and the surfaceequipment 94 may be done through a combination of communication throughthe cable, through RF transmission and through pulse telemetry.

Communication between the intermediate casing controller 102 and thesurface equipment 94 can be by any of the methods described above forthe communication between the surface casing controller 100 and thesurface equipment 94. An antenna 112 is coupled to the intermediatecasing controller 102 to allow RF communication. An acoustic transducer114 (see FIG. 8) is coupled to the intermediate casing controller 102 toallow pulse telemetry communication. Alternatively, the surface casingcontroller 100 can serve as a relay between the intermediate casingcontroller 102 and the surface equipment 94. In this situation, theintermediate casing controller 102 communicates with the surface casingcontroller 100 using any of the communication techniques discussedabove, including communicating by cable, by RF transmission or by pulsetelemetry. The surface casing controller 100 communicates with thesurface equipment 94 as discussed above.

The MWD tool sensors, actuators and generators 92 communicate with thesurface equipment 94 through a drill string controller 116. The drillstring controller 116 compiles data from the MWD tool sensors, actuatorsand generators 92 and transmits the data to the surface equipment 94.The surface equipment 94 transmits commands and other data to the MWDtool sensors, actuators and generators 92 through the drill stringcontroller 116. The communication between the surface equipment 94 andthe drill string controller 116 may be relayed through the intermediatecasing controller 102 and the surface casing controller 100.Alternatively, the drill string controller 116 may only use one of thesurface casing controller 100 or the intermediate casing controller 102as a relay. The communication between the drill string controller 116and the surface equipment 94 may use any of the information transmissionschemes described above. An antenna 118 is coupled to the drill stringcontroller 116 to allow RF communication. An acoustic transducer 120(see FIG. 8) is coupled to the drill string controller 116 to allowpulse telemetry communication.

FIG. 8 illustrates all of the communication paths possible among thevarious sensors, actuators, generators, controllers and surfaceequipment. In the preferred embodiment, the surface casing sensors,actuators and generators 88 communicate with the surface casingcontroller 100 which communicates with the surface equipment 94 overcable 96. Alternatively: (a) one or more of the surface casing sensors,actuators and generators 88 may communicate directly with the surfaceequipment 94, as indicated by dotted line 122; (b) communication betweenthe surface casing controller 100 and the surface equipment 94 may be byRF signals using antennas 104 and 106 or by pulse telemetry usingacoustic transducers 108 and 110.

In the preferred embodiment, the intermediate casing sensors, actuatorsand generators communicate with the intermediate casing controller 102which communicates with the surface equipment 94 by RF signals usingantennas 104 and 112 or by pulse telemetry using acoustic transducers108 and 114. Alternatively: (a) one or more of the intermediate casingsensors, actuators and generators 90 may communicate directly with thesurface equipment 94, as indicated by dotted line 124; (b) communicationbetween the intermediate casing controller 102 and the surface equipment94 may be by way of cable 98 (shown as a dotted line).

In the preferred embodiment, the drill string sensors, actuators andgenerators 92 communicate directly with the drill string controller 116,which may be part of an MWD tool or some other piece of drill stringequipment. The drill string controller 116 communicates with the surfaceequipment 94 through antenna 118 and/or acoustic transducer 120 directlyor using the intermediate casing controller 102 and/or the surfacecasing controller 100 as relays.

The foregoing describes preferred embodiments of the invention and isgiven by way of example only. The invention is not limited to any of thespecific features described herein, but includes all variations thereofwithin the scope of the appended claims.

What is claimed is:
 1. A casing sensor system for use in a well borehole to collect and transmit data to the surface, said casing sensorsystem comprising: a casing shoe with an outer casing having an exteriorsurface disposed proximal the well bore hole; and a casing sensor forcollecting and transmitting data to the surface, said casing sensorattached to the exterior surface of the outer casing of the casing shoe.2. The casing sensor system of claim 1 wherein: the sensor comprises apressure sensor.
 3. The casing sensor system of claim 2 wherein thepressure sensor comprises: a pressure transducer; and a transmittercoupled to the pressure transducer.
 4. The casing sensor system of claim1 further comprising: a surface receiver coupled to the transmitter. 5.The casing sensor system of claim 1 further comprising: a drill stringextending through the casing shoe.
 6. A casing sensor system for use ina well bore hole to collect and transmit data to the surface, saidcasing sensor system comprising: a casing shoe with an outer casinghaving an interior surface disposed away from the well bore hole; and acasing sensor for collecting and transmitting data to the surface, saidcasing sensor attached to the exterior surface of the outer casing ofthe casing shoe.
 7. The casing sensor system of claim 6 wherein: thesensor comprises a pressure sensor.
 8. The casing sensor system of claim7 wherein the pressure sensor comprises: a pressure transducer; and atransmitter coupled to the pressure transducer.
 9. The casing sensorsystem of claim 6 further comprising: a surface receiver coupled to thetransmitter.
 10. The casing sensor system of claim 6 further comprising:a drill string extending through the casing shoe.